101
FXCA62 TJSJ 150900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Tue Jul 15 2025

.KEY MESSAGES...

* Hot temperatures, high humidity content, and southeasterly winds
  will promote an elevated heat risk across the lower elevations
  and urban areas of Puerto Rico through the end of the week.

* Back to back tropical waves will increase shower and thunderstorm
  activity today and tomorrow.

* A Saharan Air Layer with moderate to high concentrations of
  Saharan dust will promote hazy skies and poor air quality
  conditions on Thursday and Friday.

* Increasing winds through midweek will promote choppy seas and a
  moderate risk of rip currents across most east and northern
  beaches of the islands.


&&

.SHORT TERM...Today through Thursday...

An increase in shower frequency was seen overnight across the local
Atlantic and Caribbean waters. These showers affected mainly the
islands of St. Thomas and St. John, where Doppler radar estimated
rainfall accumulations up to 0.50 inches. Nonetheless, St. Croix and
eastern Puerto Rico received some showers with limited
accumulations. Minimum temperatures were from the mid to upper 70s
along the coastal and urban areas to the upper 60s to low 70s across
the mountains. Winds were light from the east-southeast with land-
breeze variations.

A broad surface high pressure north of the area will maintain a east-
southeast wind flow today. However, winds will become from the east
by Wednesday as the surface high migrates eastward. A tropical wave
that is currently crossing the Lesser Antilles will approach the
islands today, increasing the moisture content with precipitable
water (PWAT) values between 1.80 to 2.10 inches. A second tropical
wave with its axis near longitude 50W will arrive into the area by
Wednesday bringing additional moisture into the area through
Thursday. Under the aforementioned weather pattern, showers and
thunderstorms are expected each day in the islands. During the
morning hours, scattered showers will be observed over the U.S.
Virgin Islands and eastern Puerto Rico. Then, afternoon convective
activity is likely over portions of central and western Puerto Rico,
as well downwind from el Yunque into the San Juan metropolitan area
and adjacent municipalities. At this time, there is a limited to
elevated potential to observe ponding of water in roads and poorly
drainage areas, as well as localized flooding in urban areas, roads
and small streams.

By Thursday, trailing moisture from a departing tropical wave will
continue to enhance the development of showers and isolated
thunderstorms across the islands during the day. However, a dense
Saharan Air Layer (SAL) with moderate to high concentrations of dust
particles will reach the Northeastern Caribbean and gradually moving
across the region. Therefore, hazy skies, reduced visibility, and
poor air quality conditions are anticipated through at least the
weekend.

Hot temperatures will continue to persist all week, with maximum
temperatures reaching upper 80s to low 90s along the coastal and
urban areas each day. Heat indices are expected to be above the 100
degrees Fahrenheit each day as well, with Thursday being the warmest
day. Today, there is a Heat Advisory in effect for all coastal areas
of Puerto Rico, including the Caguas Valley from 10 AM to 4 PM AST.
Residents and visitors, please be aware of these conditions and plan
accordingly if planning to do outdoor activities under sun exposure.

.LONG TERM...Friday through Tuesday...

Hazy skies, reduced visibility, and poor air quality conditions will
continue through Friday due to a lingering Saharan Air Layer.
Winds will acquire a northeasterly component as a broad TUTT-
induced trough approaches the eastern Caribbean. The combination
of the limited moisture content with daytime heating and the sea
breeze convergence will trigger afternoon showers with isolated
thunderstorms over the southwest quadrant of PR. An advective
weather pattern at night will then promote showers across the
local waters and over portions of the USVI and northeastern PR.

The TUTT-low and the induced low-level trough are expected to
move across the northeastern Caribbean through the weekend. This
will bring an increase in shower activity once again across the
islands. A tropical wave is expected to move across the region on
Monday, followed by another SAL event on Tuesday. In general,
these weather features will enhance the early morning convection
between the USVI and eastern sections of PR, followed by afternoon
thunderstorms over portions of the interior and western PR. Even
though the SAL is expected to bring hazy skies and drier mid-level
air, the precipitable water content is forecast to range between
normal to above normal levels through the end of the long-term
period.

Meanwhile, a deep layer ridge building from the central Atlantic
into the northeastern Caribbean will push further west and away of
the area the trough pattern and promote southeasterly winds by
Saturday afternoon. This moist southeast flow will prevail through
at least Tuesday, and hot temperatures are expected each day.
Likely triggering Heat Advisory conditions across most coastal
areas of PR.


&&

.AVIATION...

(06Z TAFS)

Mainly VFR conds will prevail across all terminals during the fcst
period. A tropical wave will arrive today increasing SHRA/TSRA
across the islands, affecting the TJSJ/TIST/TISX aft 15/13-14Z and
TJBQ/TJPS aft 15/17-18Z. Brief MVFR cigs possible btw 15/17-23Z. ESE
winds expected btw 15-20 kt with sea breeze variations and higher
gusts aft 15/13Z.


&&

.MARINE...

A surface high pressure will strengthen over the western Atlantic
early this week. Back to back tropical waves will move across the
local waters today and on Wednesday. Therefore, moderate to
locally fresh trades and choppy seas are expected across the
regional waters through midweek. Increasing shower and
thunderstorm activity is expected with the passage of the tropical
waves. Hazy conditions due to Saharan dust are expected on
Thursday and Friday.


&&

.BEACH FORECAST...

There is a moderate risk of rip currents for the north and east
facing beaches of Puerto Rico, Culebra, Vieques, and St. Croix.
Life-threatening rip currents often occur in the vicinity of
groins, jetties, reefs, and piers. The potential for isolated
thunderstorm development will increase today and tomorrow across
most coastal areas due to passing tropical waves.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ001>005-007-008-010-011.

VI...None.
AM...None.
&&

$$

SHORT...GRS
LONG...DSR